1. Field
The present disclosure relates to a neutral atom trapping device with high optical depth for quantum optics experiments.
2. Background
Since laser cooling and trapping was developed in 1980's [E. L. Raab, M. Prentiss, A. Cable, S. Chu, and D. E. Pritchard, Phys. Rev. Lett. 59, 2631 (1987)] that led to the Nobel Prize in Physics in 1997, the magneto-optical trap (MOT) has been widely applied and implemented to provide cold atom sources for scientific researches in the field of atomic physics and quantum optics. Many cold atom devices have been invented for possible applications in atomic sensors and some of them have been commercialized [See ColdQuanta Inc; D. Z. Anderson and J. G. J. Reichel, US Patent 2005/0199871; D. Z. Anderson et al, US Patent 2010/0200739; M. Hyodo, U.S. Pat. No. 7,816,643 B2]. The most commonly used cold atom device is the three-dimensional (3D) MOT with a configuration of six trapping laser beams and a 3D quadrupole magnetic field where the cold atoms are trapped at the position of zero magnetic field spherically. In that configuration, there is only one point of zero magnetic field and the atoms experience magnetic gradients along every direction. Therefore, for experiments and applications which require long atomic coherence time, such as electromagnetically induced transparency (EIT), atomic quantum memory, and single-photon generation, the magnetic field must be switched off before the experimental time window [A. Kuzmich, W. P. Bowen, A. D. Boozer, A. Boca, C. W. Chou, L.-M. Duan, and H. J. Kimble, Nature 423, 731 (2003).]. This significantly adds complicity in the controlling system and prevents the experimental data collected from a high repetition rate because it always takes time to switch off the current in a magnetic coil due to the inductance. The quantum optics and photon counting experiments based on the 3D MOT are typically time consuming.
One approach changes a 3D quadrupole magnetic field to a 2D quadrupole magnetic field with a line of zero magnetic fields. This is called a 2D MOT where the cold atoms are trapped in the zero magnetic field line along the longitudinal symmetry axis. There are two configurations in the conventional 2D MOT devices. In the first configuration, there are only 4 trapping laser beams transmitted perpendicularly to the longitudinal axis [T. G. Tiecke, S. D. Gensemer, A. Ludewig, and J. T. M. Walraven, Phys. Rev. A 80, 013409 (2009)]. As a result, the cooling and trapping occur only two-dimensionally and there is no cooling and trapping along the longitudinal symmetry axis where the atoms are free to move. In the second configuration, two more counter-propagating trapping laser beams are added along the longitudinal axis to provide the additional cooling in the third dimension [K. Dieckmann, R. J. C. Spreeuw, M. Weidemuller, and J. T. M. Walraven, Phys. Rev. A 58, 3891 (1998)]. In that setup, the optical accesses along the longitudinal symmetry axis are blocked or shared by the two trapping beams along that direction. The conventional 2D M
High optical depth (OD) is sought for much quantum optics research [A. V. Gorshkov, A. Andre, M. Fleischhauer, A. S. Sorensen, and M. D. Lukin, Phys. Rev. Lett. 98, 123601 (2007)], but in the traditional MOT optical configuration high OD is commonly obtained by increasing the MOT size where more cold atoms can be obtained in the cloud. But the MOT size is usually determined by the MOT laser beam size which is limited by the total laser power. Another way to improve the OD is increasing the atomic density in the cloud using a dark-spot configuration [W. Ketterle, K. B. Davis, M. A. Joffe, A. Martin and D. E. Pritchard, Phys. Rev. Lett. 70, 2253(1993)], but the magnetic field gradient is often required to switched off for applications. Also, in conventional 2D MOTs, there is a limitation for optical access due to its geometry and the OD may need to be further improved.